Since the beginning of this project we have screened over 3000 subjects for this study. We have enrolled approximately 210 youth with bipolar disorder (BD), 310 subjects at risk for BD because they have a parent or sibling with the illness, and 115 adults with BD. This year, approximately 25 new subjects were enrolled. This year we continued our work designed to identify the brain mechanisms underlying BD in children; compare brain function in youth and adults with BD in order to begin to understand how the illness develops over time; and compare brain function in youth at familial risk for BD to those with BD and those at low risk, in order to facilitate the eventual development of preventive interventions. Regarding our work on the brain mechanisms mediating BD, much of that work consists of, not only comparing youth with BD to healthy youth, but also comparing youth with BD to those with severe, chronic irritability (the so-called Disruptive Mood Dysregulation, or DMDD, population, see Annual Intramural Research Report ZIAMH002786). It is important to compare youth with BD and those with DMDD because, particularly before the inclusion of DMDD in the DSM-5, irritable children frequently received the diagnosis of BD in the community, despite not having a history of manic episodes. This potential misdiagnosis is important because, compared to severe, chronic irritability, BD in youth is treated with medications with high side-effect burden. While it is possible that the addition of DMDD to DSM-5 has decreased the extent to which irritable children are misdiagnosed as having BD, nonetheless it is important to differentiate the brain mechanisms underlying each of these clinical presentations, because differences between the diagnoses may be relevant to treatment approaches. For example, in work published this year, we compared brain activity in youth with BD vs. those with DMDD during a task that involved subjects labeling face emotions. The results of that study are described under ZIAMH002786. Data from this study suggest that targeting aberrant responses to angry faces might be an effective treatment for severe irritability, whereas such an approach might be less likely to be effective in youth with BD. Last year, we published work comparing BD, DMDD, and healthy youth using resting state imaging techniques. Such techniques are designed to study brain function while subjects are resting and thus to identify intrinsic functional connectivity amongst brain regions. This year we extended our resting state connectivity work with another study examining connectivity in youth and adults with BD, both comparing them to healthy subjects and examining age effects. Thus, this study is consistent with our goals of elucidating the brain mechanisms mediating BD, while also comparing such brain mechanisms between adults and youth with BD. Our most recent work also represented a methodological advance over prior work in that, rather than simply examining amygdala connectivity, we used more sophisticated techniques to compare connectivity among all brain regions. Compared to healthy subjects, patients with BD showed dysconnectivity in two networks: a temporal-parietal network involved in late stages of visual processing, and a cortico-striatal network involved in attention, cognitive control, and response generation. There were no significant differences between youth and adults with BD, but this conclusion must be tempered by the relatively small size of the sample. Across our bipolar disorder-related groups (adults with BD, youth with BD, youth at risk for BD), face emotion processing has been a major focus. This is because deficits labeling face emotions accurately, as well as deficits in face emotion memory, are present, not only in patients with BD, but also in youth at risk for the disorder. These findings indicate that such deficits in face emotion labeling and memory are potential endophenotypes for BD. This year we published two relevant papers, and a third is under review. In the first, we found that both youth with BD and those at risk for the disorder showed parahippocampal dysfunction while processing emotional faces, suggesting a possible neural endophenotype. In the second paper, we compared neural connectivity in adults with BD vs. healthy volunteers while subjects processed emotional faces consciously and unconsciously. We found that, when viewing faces that were unconsciously vs. consciously perceived, BD exhibited decreased functional connectivity between the amygdala and ventrolateral prefrontal cortex (vlPFC), whereas healthy subjects exhibited the opposite pattern. Aberrant amygdala-vlPFC connectivity has been a major focus of the literature that uses face emotion processing tasks to study the brain mechanisms of BD. These results suggest that such findings may differ with the extent to which the face emotion processing is conscious vs. unconscious. Finally, in the third face emotion processing study, which is currently under review, we compared youth with BD, those at risk for BD, and healthy subjects while they labeled face emotions. We found three patterns of results. Candidate risk endophenotypes (i.e., where BD and HR shared deficits) included dysfunction in higher-order face processing regions (e.g., middle temporal gyrus, dorsolateral prefrontal cortex). Candidate resilience markers and disorder sequelae (where HR and BD, respectively, show unique alterations relative to the other two groups) included different patterns of neural responses across other regions mediating face processing (e.g., fusiform), executive function (e.g., inferior frontal gyrus), and social cognition (e.g., default network, superior temporal sulcus, temporo-parietal junction). In addition to deficits in face emotion processing, another potential behavioral endophenotype that we have identified in BD is increased intrasubject variability in reaction time (ISVRT). ISVRT is thought to represent attentional lapses, and we have identified increased ISVRT in both preschool and school-aged youth at risk for BD. In a manuscript that is under review, we performed an fMRI study of school-aged youth at risk for BD, and healthy youth. The study used a neuroimaging task designed to identify the brain regions mediating increased ISVRT in youth with, or at risk for, BD. Specifically, the technique allowed us to examine associations between reaction time and brain activity on a trial-by-trial basis. We found blunting in key frontal, cingulate, and striatal areas in unaffected, at-risk individuals and in euthymic patients with BD. This blunting partially mediated group differences in reaction time variability, thus suggesting possible brain mechanisms mediating the ISVRT that has been identified in both youth with BD and those at risk for the disorder.